Lapping machine



July 1, 1947.

M u m N July l, 1947 M. RAMsAY 2,423,118

LAPPING MACHINE Filed Feb. 5, 194e s sheets-sheet 2 Y il 20 2 ,Z4 Z

@Umea INVENTOR /YABCUJ /GA/UAY h M. RAMs/w LAPPING MACHINE Filed Feb. 5. 1946 July l, 1947.

5 Sheets-Sheet 3 2 f 7//////////////////////////////////// l7//////l//////////////////X INVENTOR IA'QCU A MJA Y BY oRNEY ILPIING MAC Marcus Ramsay, New York, N. Y., assigner ai Lid per cent to Eric G. Ramsay and 20 per cent to lill. Dorsey Spencer, both of New York, N, Y;

Application February 5, 1946, Serial No. 645,644

i6 Claims. (Cl. 51-16l) This invention relates to lapping machines and in the manner just described has proved to be particularly to lapping machines designed to very satisfactory for oscillators oi the frequencies finish to required thickness dimensions relatively heretofore most commonly used, particularly bethin articles, usually having parallel faces, such cause of the ability to keep a check on the linas piezo-electric quartz crystals of the type used 5 ishing operation by devices which may measure to control the frequency or wave length of radio the oscillations which are set up in the blanks broadcasting sets or stations. as an incident to the lapping operation. When, in the manufacture of quartz oscillators for however, it comes to lapping quartz oscillators. controlling the wave lengths of radio broadcastparticularly of the AT and BT cuts, to a thining sets, etc., it is customary to cut the blank l0 ness which will permit their use for the higher for the oscillator, at the required inclinations frequencies now being employed in many iields, to the various axes oi the quartz crystal, to a for example, to a finished thickness vof .003 of thickness considerably greater than that desired an inch or under, it will be apparent that one in the finished oscillator, in order to provide of the first diiiiculties encountered, if the method sumcient leeway for nishing the surfaces of and means `just described are to be employed, the blank to the required degree of smoothness is to provide a work holder that is of a thickand at the same time to provide for such alterness suiliciently less than the finished thickness ations as may be necessary to attune the blank of the oscillator to permit both faces of the osto the desired frequency and to insure a high cillator blank to remain in contact with the lapdegree of activity. In cutting and nishing ping surfaces of the two lapping plates to the oscillators for the higher frequencies, for eX- end of the lapping operation. This has proved ample, the so-called AT and BT cuts, considerto be a practically insurmountable obstacle to the ation must be given to the fact that the frelapping of oscillators to the extremely low thickquency is a function of the thickness of such nesses above referred to by the means above a cut, i. e. the thinner the oscillator the higher described.

its frequency. A general object of the present invention,

In the lapping of oscillator blanks substantherefore, is to provide improved means for laptially to iinished dimensions, as heretofore pracping quartz oscillator blanks or the like substanticed, it has been customary to place the blanks tially to their nished thicknesses which will in openings in a relatively thin work holder permit the lapping of blanks substantially to any located between two lapping plates, the opendesired degree of thinness. More particularly. ings in the work holder 4being each designated the invention aims to provide means for lapping to receive and loosely confine a single blank and oscillator blanks or the like substantially to any the Work holder itSelf being given a @OmpleX desired degree of thinness which retains the prinrotating and revolving movement between the ciple of the insulating Work holder between the lapping plates such that a suitable lapping rellapping plates whereby the degree of thinness i ative movement of the blanks to the plates will obtained, that is, the approximation to the high be brought about. Where the work holder is frequency desired, can be followed throughout designed for use in lapping rectangular blanks the lapping operationen a suitable frequencyV itis customary to make the blank-receiving openindicating instrument connected to the laps.

ings pentagonal in shape so that the combined With the foregoing and other objects in view;

revolving and rotating movement of the work the invention contemplates the provision of a holder between the lapping plates will bring about lapping machine having a work holder provided a turning of the blanks in the openings therein with an article-receiving opening or openings to insure a uniform lapping action over the two therein to receive and loosely confine the article faces of each blank. Furthermore, in order that or articles the opposite faces of which are to be the extent of the lapping may be followed by lapped, this work holder being arranged to hold frequency measuring devices connected to the the article or articles to be lapped in lapping relalaps while the lapping is taking place, these tion to two relatively movable lapping members, work holders are usually made in whole or in one of which has a lapping surface of an area part of some good insulating plastic and of course sufficient to continue in lapping engagement with must be of a thinness less than the desired iinone face of an article or articles in the work ished thinness ofthe blanks to be lapped therein. holder throughout the relative travel of said work The nishing of quartz oscillator blanks subholder and of said lapping member during the stantially to their desired frequencies by lapping lapping operation and the other lapping member having a portion or portions thereof shaped to enter the article-receiving opening or openings in the work holder, to bear upon the article or the articles to -be lapped in said opening or openings and to cause said work holder to partake of the relative movements of said lapping members, the article-engaging face or faces of the portion or portions of said lapping member which enter said work holder opening or openings being constructed to serve as the lapping surface or surfaces for the article face or faces engaged thereby. By thus causing the part or parts of one lapping member which has or have thereon the lapping surface or surfaces of said member to enter into the article-receiving opening or openings in the work holder and thus engage and press the article or articles into lapping engagement with the other lapping member, while causing the work holder to partake of the relative movement of the I lapping members, the thickness of the word holder is made independent of the ultimate thickness oi' the finished oscillator,

The present invention thus makes possible retaining all of the advantages of work holders of insulating material which maintain the lapping plates in insulated relation to each other while permitting the lapping surfaces of said plates to be kept in lapping engagement with the opposite faces of the oscillators throughout a lapping operation which is capable of producing oscillators of substantially any desired thinness. With such an arrangement it is obvious that the existing method of following the extent to which the lapping has proceeded by means of oscillation detectors connected to the laps can also be practiced.

Other objects, important features and advantages of the invention, to which reference has not specifically been made hereinabove, will appear hereinafter when the following description and claims are considered in connection with the accompanying drawings, in which- Figure 1 is a front elevation, partly in section, of that part of a lapping machine of the drill press type in which the invention is shown as embodied, the section being taken on the line I--I oi Figure 2;

Figure 2 is a horizontal section on the line 2-2 of Figure 1;

Figure 3 is a plan view, with parts broken away, showing particularly the construction and arrangement of the upper and lower laps and of the work holder;

Figure 4 is a detail section on the line 4-4 of Figure 3;

Figure 5 is a detail section on the line 5 5 of Figure 2:

Figure 6 is a detail sectional view showing part of the work holder, part of the upper lap and part of the lower lap;

Figure 7 is a perspective view of one of the work-engaging lingers of the upper lap removed" from its carrier and inverted;

Figure 8 is a plan view of the upper and lower laps and of the work holder in a modified embodiment of the invention;

Figure 9 is a vertical section on the line 9-9 of Figure 8; l

Figure 10 is a plan detail showing the clearance between the sides of a work-engaging nger of the upper lap and the associated article-receiving opening of the work holder which is sometimes desirable in a machine of this type designed to carry out the earlier stages of the lapping operation,l and Figure 11 illustrates a modified finger construction particularly designed for use in lapping circular oscillators.

As suggested in the above brief description oi' the figures of the drawings, the invention is shown as embodied in a lapping machine of the so-called drill press type, that is, a machine in which the annular stationary lap 2 is mounted upon the drill press tablel 4 and the lapping movement is brought about by a crank pin 6 carried on an eccentric received in a socket in an arm I0' on the drill shaft I2 which is vertically movable in the post I4 by the usual connections to a handwheel I5. A clamp I6 and clamp screw Il may secure the shaft I2 in its elevated or withdrawn position. The eccentric 8 is held in its adjusted position in the socket in the arm I0 by a set screw I8 which permits adjustment of the crank pin 6 to different radial vdistances from the axis of the shaft I2.

As hereinabove pointed out, in the usual type of drill press lap, both the lower and the upper laps are held stationary and the work holder is moved between the laps by a suitable connection to the crank pin 6. The present invention, in order to attain its object of making the ultimate thickness of the oscillator independent of the thickness of the work holder, moves the work holder and the upper lap together and provides for telescoping of the parts of the upper lap on which its lapping surfaces are formed into the work-receiving opening or openings in the workholder, whereby the lapping surfaces of the upper lap may bear constantly upon the upper faces of the oscillator blanks to be lapped and remain in lapping contact therewith, regardless of the thickness of the work holder, down to any desired degree of thinness of the oscillators. As herein shown, the work holder 20, the thickness of which is independent of the ultimate thickness of the lapped crystal and is only limited by the requirements for convenience in manipulating the oscillator blanks in the openings therein, is provided with crystal-receiving openings 22 which may be of the usual pentagonal shape and of the usual size of such openings in work holders heretofore employed, each opening being designed to receive a single rectangular crystal or oscillator blank and being sulllciently larger than the crystal so that the crystal can turn freely in the opening during the lapping operation, the engagement of the corners of the crystal with the sides of the pentagonal opening 22 tending to cause the crystal to rotate in its own plane as it is rubbed between the lapping surfaces during the lapping operation. 'Ihe work holder 20 rests upon the lower lapping plate 2 which, as shown, may be provided with the usual transverse grooves 24 which serve two purposes, (l) to receive and partially contain the lapping abrasive and the liquid used therewith and (2) to prevent the formation of a vacuum between the plate and the crystal suilicient to interfere with its movements over the plate.

The upper lapping member, instead of comprising a stationary plate similar to the lower plate 2, as in the drill press type of lapping machine of the prior art, comprises an annular carrier plate 26, which need not be the lower lapping plate having projecting from of as large diameter as 2, the carrier plate 28y its lower face lingers 2l which substantially fit the pentagonal openings 22 in the carrier 20 so that they may be partly telescoped thereinto and which have lapping surfaces 30 on their lower ends, that is, on the ends which engage the upper faces of the crystals 32 in the holder openings 22. These fingers 28 may be mounted in the carrier 26 in any suitable manner, as, for example, by being provided with cylindrical stems 34 suitably secured in correspondingly shaped openings 36 drilled into the-carrier plate 26.

From the foregoing description it will be seen that the projection of the fingers 28 of the upper lap member 26 into the openings 22 of the work holder 2d necessarily compels the work holder 20 to follow the movements of the upper lap member 26. To bring about these movements, a plate 38, having an annular dependent flange or rib 40, is mounted on the upper side of the lap member 26, the rib Ml fitting within the central opening 42 in the annular lap member 26. Preferably the rib tu fits snugly within the opening 42 so that there is little or no tendency to relative rotary movement of the plate 38 and the lap member 26.

The plate 3B has at its center a bearing opening for the pin 6, which opening is provided with a bushing M of insulating material to insulate the upper lap member from the machine proper on which one side of the oscillation detecting circuit, hereinafter to be described, is grounded. It will be seen from Figure '7 that the faces 30 of the fingers Ztl are likewise provided with grooves it which serve the same purpose and act in the same manner as the grooves 24 of the lower lap 2. The lower lap 2, as shown in Figure 2, is secured against rotation or other movement by positioning plates 48 having elongated openings du therein through which screws 50 may be screwed into the table 4 to secure the plate 2 in its properly adjusted relation to the other parts of the machine.

From the foregoing description it will be seen that, when the shaft i2 is rotated by any suitable drill press driving mechanism, the crank pin 6 on the arm i@ will be revolved about the axis of the shaft i2 and will thus bodily move the center of the upper lap member 25 and the work holder 2li in a circle having a radius corresponding to the distance of the axis of the crank pin 6 from the airis of the shaft l2. This bodily movement of the upper lap 2li and the work holder 2li about the axis of the shaft i2 will also effect a gradual rotation of the upper lap 25 and the work holder 2li about the axis of the crank pin t: The more or less planetary movement thusl produced willA obviously effect a complex relative movement of the crystals 32 in the pentagonal openings 22 between the lapping surfaces of the lingers 28 and the lower lap plate 2, by reason of the rotation of the crystals in the openings 22, with the result that both faces of the crystals 32 will be gradually abraded.

Because of the greater travel which the lower faces of the crystals 32 make over the lapping surface of the plate 2, it will be apparent that the major part of the abrasion will take place on said lower faces. In actual practice it is estimated that from 90 to 95% of the abrasion of a crystal in this stage of the lapping operation takes place on the lower face and that from 10 to takes placeupon the upper face. By simply turning the crystals over before the lapping is completed, any deficiency in lapping results which might result from the difference in lapping effects on the two faces can be equalized. It is customary in any event, in lapping crystals, to transfer the crystals from one side to the other of the work holder to prevent theirA being lapped into wedge shapes.

` advantages are obtained by this arrangement, i

It will be noted from an inspection of Figure 7 that the grooves 46, having the purposes hereinabove set forth, are shown as radiating from the center of the lapping face 30 of the finger 28. Although the invention is not restricted in any way to this arrangement of the grooves 46 shown in Figure 7, it is. believed that certain since the relative movement of the lapping surface 36 and the crystal 32 is principally a movement brought about by the rotation of the crystal 32 in its own plane in the pentagonal opening 22 in the work holder 20, there being little of Vthe bodily travel of the crystal 32 over the lapping surface 30 of the finger 28 such as that over the lapping surface of the plate 2 brought about by the relative movement of the work holder 20 and the plate 2.

In the modified embodiment of the invention shown in Figures 8 and 9, the upper lap member, instead of being provided with a `plurality of spaced fingers arranged to enter and partially telescope into correspondingly spaced and shaped openings in the work holder. is formed as a continuous annular member 52 which is adapted to t within a corresponding annular opening 54 in a work holder made up of' two pieces, one of which is an outer ring 56 surrounding the annular lap member 52 and the other of which is a disc-like member 58 adapted to fit within the annular lap member 52. In this embodiment of the invention the lower lapping plate 2 is of the same annular construction as in the embodi ment of the invention first described` To connect the annular upper lap 52 to the crank pin 6, in order to effect the lapping movement thereof over the lapping plate 2 and at the same time f to move the two-part work holder 56 and 58 with it, a crossbar 66 is provided which extends diametrically across the member 52 and is connected thereto in any suitable manner, as by means of dowels t2. The crossbar @il has a crank pin receiving opening t@ at its center which is provided with an insulating bushing 65 so that the upper lap is insulated from the lower lap, the two parts 56 and 58 of the work holder being preferably formed of insulating material, atleast on their lower faces.

It will be noted that the crystals or oscillator blanks 32 are not segregated from each other in this embodiment of the invention as they are in the embodiment first described and therefore the edges of the crystals are apt to be brought into contact with each other during the lapping operation. It will be obvious, therefore, that this embodiment of the invention is better suited to the lapping of oscillator blanks that are circular in contour rather than rectangular.

It is customary in lapping machines of the drill press type so to move the work holder with respect to the laps that the crystals will at certain stages of their movements slightly project over the inner edges and at other stages over the outer edges of the annular lap members, thus preventing the formation of marginal ridges on the laps as their faces are worn away. This provision for overlapping the lap edges is obviously more important in the initial lapping steps where the coarser lapping powders are used.

It will be seen that such overlapping of the inner and outer edges of the lower lap 2 may also be brought about in the embodiment of the invention shown in Figures l to 7 inclusive by so adjusting the crank pin 6 that the swing thereof will move the holder 20 to such an ex# and horizontally.

tent as to cause a slight overlap of the crystal lower lap 2 while the crystal 32 in the opposite opening 22 is carried over the inner edge of said lower lap. This overlap should, of course, be relatively small to avoid breakage of the crystal by the pressure of the oil or other liquid thereon, the amount permissible being determined somewhat by the thickness of the crystal. When effecting the final lapping, however, that is, to bring the crystals down to the extreme thinness required for very high frequency oscillators, it will probably be desirable not to allow any overlap. In such cases it will probably be necessary to re-lap the lapping surfaces themselves more frequently between operations to insure parallelism of these surfaces.

Where the formation of marginal ridges on the lingers 28 is to be avoided, a slight lateral clearance is provided between the sides of each nnger 28 and the sides of the pentagonal opening 22 in the work holder 20. 'Ihis permits suilicient overlapping of the crystal 3,2, in its rotating movements in the opening 22, over the edges of the lapping surface 30 of the finger 28 to avoid the grinding of a marginal ridge upon the lapping face 30.

Such clearance is shown in Figure 10 of the drawings, but, as above stated, is usually not required or desirable for the last lapping step.

Likewise, as shown in Figure 9 of the drawings, a slight clearance may be provided in the opening 54 between the walls thereof and the sides of the lap 52 to permit sufllcient overlap of the crystals 32 in the lapping operation to'prevent the grinding of marginal ridges on the lapping face 53 of said lap 52.

Although the usual crystal oscillator now manufactured is of rectangular contour,` some experlmentation has been carried on with crystals of circular contour. If crystals of circular contour are to be lapped in a lapping machine embodying the present invention, in the form thereof in which each crystal is confined in an individual work holder compartment 22, it would not be necessary in such a case to have this opening of the pentagonal form shown in Figure 6.- Instead, the crystal-receiving opening in the Work holder might be circular, as shown at 68 in Figure 11, and the finger 10, which ts Within the opening .68, would likewise be of circular sectional contour. To avoid forming a central ridge or elevation on such a finger its lapping face 12 might be in annular form, with a hollow* center 14, and the round crystal 32 might be of such diameter as slightly to overlap the inner edge of the annular face 'I2 to avoid forming an inner marginal ridge on the face l2.

From'the foregoing description it will be seen that the present invention provides simple and eilicient means for lapping crystal oscillators, particularly of the AT and BT cuts. to thinnesses not attainable by lapping means heretofore employed. It will be understood, of course, that the invention is not. restricted to the embodiments herein illustrated and described and that many variations thereof, especially such as are adapted to meet particular conditions, may be.

made without departing from the principles of operation of the improved lapping means defined in the appended claims.

What I claim as new is:

1. In a lappingmachine of the class described. the combination with opposed lapping members movable relatively to each other both vertically of a work holder having an article-receiving opening therein to receive and loosely conne an article the opposite i'aces of which are to be lapped, one of said lapping members having la lapping surface of an area sumcient to remain in lapping engagement with one face of an article in the work holder throughout the relative travel of said work holder and y said lapping member during the lapping operation and the other lapping member being shaped and arranged to enter the article-receiving opening in said work holder and to bear upon the opposite face of the article to be lapped, whereby said work holder and said last mentioned lapping member move together throughout lapping travel of the work holder and the first mentioned lapping member.

2. A lapping machine according to claim 1 in which the work holder has a plurality of spaced openings, each adapted to receive and loosely confine an article the opposite faces of which are to be lapped, and in which one of the lapping members is provided with fingers adapted to enter the work holder openings and to press the articles therein into lapping engagement with the other lapping member, said fingers having lapping surfaces on their article-engaging ends.

3. A lapping machine according to claim 1 in which the portion of one lapping member that enters the article-receiving opening in the work holder has a. contour corresponding to that of the opening and approximately filling the opening.

4. A lapping machine'according to claim 1 in which the work holder is provided with a plurality of individual article-receiving openings and one of the lapping members is provided with a corresponding plurality of finger-like projections approximately fitting within said openings and having lapping surfaces on their article-engaging ends, the fit of said fingers within said openings being suiilciently loose to prevent the formation of marginal ridges on the lapping surfaces thereof as a result of the lapping action.

5. A lapping machine according to claim 1 designed for lapping articles of rectangular contour in which the work holder is provided with a plurality of polygonal individual article-receiving openings and in which one lapping member has a plurality of correspondingly shaped fingers adapted substantially to fit within said openings and provided on th'eir article-engaging ends with lapping surfaces.

6. In a lapping machine of the class described,

the combination with opposed lapping members and meansy for effecting relative lapping movements thereof, of a work holder provided with spaced openings therethrough to receive and loosely conne, in separated relation to each other, articles the opposite faces of which are to be lapped, one of said lapping members having a lapping surface of' an area, sufficient to engage simultaneously, throughout the lapping operation, the faces of all the articles to be lapped which are exposed on one face of said work holder and the other lapping member being provided with ngers adapted to enter the Work holder openings and to press the articles therein into lapping engagement with the other lapping member, said fingers having lapping surfaces on th'eir article engaging ends.

7. A lapping machine according to claim 6 in which the fingers approximately t the openings in the work holder.

8. A lapping machine according to claim 6 in which the fingers approximately fit the openings in the work holder but in which' there is sumcient looseness of t to prevent the formation of marginal ridges on the article-engaging ends of the fingers by reason of the lapping operation.

9. A lapping machine according to claim 6 intended for lapping articles of rectangular contour in which the work holder openings are of polygonal contour and the fingers are of a corresponding sectional contour of approximately like dimenslons.

lil. .A lapping machine according to claim 6 intended for lapping articles of' rectangular contour in which the openings in the Work holder are f equilateral pentagonal contour and the fingers are of a like sectional contour of approximately equal dimensions.

11. A lapping machine according to claim 6 in which the work holder openings are of circular contour and the fingers shaped to fit closely therewithin, the lapping surfaces on the ends of the ngers being of annular contour.

12. A lapping machine according to claim 1 in which the lapping member which is movable with the work holder is arranged above the other lapping member so that gravity serves to maintain it constantly in engagement with the upper face of the article to be lapped.

i3. A lapping machine according to claim 6 in which the lingered lapping member is arranged above the other lapping member so that gravity serves to maintain the fingers thereof in pressing relation to the articles to be lapped respectively engaged thereby.

14. In a. lapping machine of the class described, the combination with opposed lapping members and means for effecting relative lapping movements thereof, of a work holder having an articlereceiving opening therein to receive and loosely confine an article the opposite faces of which are to be lapped, one of said lapping members having a lapping surface of an area suincient to remain in lapping engagement with one face of an article in the work holder throughout the relative travel of said work holder and said lapping member during the lapping operation and the other lapping member having a portion thereof Shaped to .enter the article-receiving opening in said work holder, bear upon the opposite face of the article to be lapped, and to cause said work holder to partake of the relative movements of said lapping members, the article engaging face' of the portion of said lapping member which enters said work holder opening being constructed to serve as a lapping face.

15. In a machine for lapping piezo-electric crystals to insure high activity and approximate face parallelism, the combination with opposed parallel-faced laps, between the lapping faces of which a crystal to be lapped may be placed, of a work holder arranged for crystal-lapping relative movement over one lap and having a workreceiving opening therein in which the crystal and the other lap are laterally confined for limited relative lapping movement in respect to each other during the crystal-lapping relative movement of the work holder and the rst mentioned lap, the laterally conned lap being freely movi able in said holder toward the other lap.

16. The process of lapping piezo-electric crystals to insure high activity and approximate face parallelism for any desired thickness, which consists in placing the crystal to be lapped between two parallel-faced laps, laterally conflnins the crystal and one lap to limited relative lapping movement while permitting free movement of said lap toward the other lap and then eiecting a crystal-lapping relative movement ot said laterally confined lap and crystal in respect to the other lap.

MARCUS RAMSAY. 

